Apparatus for unloading bulk material

ABSTRACT

A device for mechanically connecting hopper car unloading boots to the discharge outlets on the car for unloading bulk material from the car, in which the lift platform for raising the boots is held level with the car and pressure is exerted evenly on the platform in order to maintain full contact with discharge outlets while the material is being unloaded.

United States Patent Pase APPARATUS FOR UNLOADING BULK MATERIAL 1451Feb. 11,1975

FOREIGN PATENTS OR APPLICATIONS 2| 1,98l ll/l960 Austria 254/l22 [75]Inventor: Hugh H. Pase, Cheshire, Conn. l,9l2.640 9/1970 Germany 254/122[73] Assignee: Mimco Incorporated, Meriden. D

Conn. Primary Exammer-Al Lawrence SmIth Assistant Examiner-Robert C.Watson Flledi 171 1972 Attorney, Agent, or Firm-Steward & Steward [2]]Appl. No.: 307,445

[57] ABSTRACT [52] U.S. Cl. 254/124 A device for mechanically connectinghopper car un- [Sl] Int. Cl B66! 3/00 loading boots to the dischargeoutlets on the car for [58] Field of Search 254/l0 C, 124, 122 unloadingbulk material from the car, in which the lift platform for raising theboots is held level with the car [56] References Cited and pressure isexerted evenly on the platform in UNITED STATES PATENTS order tomaintain full contact with discharge outlets 2 554 494 5/1951 Hodgin254/122 is bemg 2920373 l/l960 Knabe 254/l0 C 7 Chims' 5 Drawing Figures3,112,676 l2/I963 Boulsover 254/122 so. I so IE 1a '9' 12 I8 98 96 97 ,1l I. 1| ll s2 20* 1 e6 e2 PATENTH] FEB] l 1975 SHEET 10F 4 ll/l/l/Vld m.ro

PFJENTED 186E347 SHEET 20$ 4 FIG.3

PATENTEB FEB! 1 I975 SHEET 30F 4 PATENTED 1 3.865.347

sum a nr 4 1 APPARATUS FOR UNLOADING BULK MATERIAL BACKGROUND OF THEINVENTION The present invention relates to apparatus for unloading bulk,material-carrying cars such as railraod hopper cars and the like, and itrelates more particularly to improvements in unloading apparatus of thetype shown in my prior US. Pat. No. 3,528,570 granted Sept. I5, 1970,wherein a movable platform is supported on the free ends of lifting armswhich are pivoted to a fixed frame at the unloading station. One end ofa boot or tubular chute for receiving the material as it flows from theoutlet of the car is fastened to the platform, so that when the liftingarms are swung upwardly by a power cylinder the movable platform andboot are raised into engagement with the discharge outlet of the car inorder to connect the boot thereto and to hold it in sealing engagementtherewith. Such unloading apparatus has saved a great deal of drudgerywork required where the boot must be connected to the discharge outletmanually.

However, as in the case of most new products, certain problems have beenencountered with unloading apparatus of this type. One of them has beendifficulty in preventing the lift platform from tilting to one side orthe other as it is raised or lowered. While leveling devices have beenprovided in order to prevent such tilting, they have not always beensatisfactory due to the fact that they are exposed to the dust, grit andthe caking of the materials being unloaded, such as cement, which hassometimes prevented them from functioning properly.

An object of the present invention is to provide an improved type ofleveling device for unloading apparatus of the kind shown in myabove-mentioned patent, which is mechanically simple and which will workproperly under the most adverse conditions. Another object of theinvention is to equalize the force exerted by the lifting arms, in orderto maintain sealing engagement between the movable platform and thedischarge outlet of the car being unloaded.

SUMMARY OF THE INVENTION Basically the invention resides in providing aleveling device for the movable platform, which includes relativelyrigid members pivotally connected together to form a collapsibleparallelogram, said members being arranged in such a way that themovable platform and the fixed frame of the unloader in effect form twoparallel sides of the parallelogram, thereby tending to prevent themovable lift platform from tilting with respect to the fixed frame.However, since the forces exerted on the lift platform are not alwaysevenly distributed, as for example when a rigid object is disposedbetween one side of the lift platform and the discharge opening of thecar, preventing that side of the lift platform from moving into fullengagement with the discharge opening while the other side is free tomove, a strain is placed on the entire construction, including thedevice for holding the lift platform level as well as the lift platformitself. An important aspect of the present invention, therefore, residesin the provision of a safety device which will harmlessly release theleveling device in the event the lift structure is placed under atilting stress of sufficient magnitude to cause permanent damage to anypart of the structure.

More specifically the invention resides in providing a leveling devicewhich includes members that are separate from the lifting arms and themovable lift platform but are connected thereto in such a way that anyforces exerted on the platform tending to tilt it out of parallel withthe fixed frame of the unloader are transmitted to the leveling device.The platform and lifting arms can, therefore, be retracted when theplatform is lowered into substantially co-planar relationship, while theleveling device remians in a somewhat raised position so that theparallelogram does not collapse when the platform is fully retracted andsubstantially flush with the fixed portion of the frame. As will be moreapparent hereinafter, this arrangement ensures that the leveling deviceremains effective, in preventing the platform from tilting when it isfirst raised, as well as when it is fully extended and contacting thedischarge opening on the car and at all points intermediate its fullyretracted and fully extended positions.

Another important aspect of the invention resides in providing a liftingassembly for a bulk unloading apparatus of this kind in which the forceexerted by each of the lifting arms is equalized despite the fact thatthe power means for raising the lifting arms is located at only one sideof the lifting assembly.

DESCRIPTION OF SPECIFIC EMBODIMENT The invention is illustrated in theaccompanying drawings wherein FIG. I is a side elevation of a bulkunloading apparatus in which the leveling device of the presentinvention may be employed and showing the boot-connecting assemblyelevated into full engagement with the discharge outlets on theunderside of a railroad hopper car;

FIG. 2 is a broken side elevational view of only the lifting andleveling linkage for the unloading apparatus of FIG. 1 shown in itsfully retracted position with the lift cylinder and crank arm on oneside broken away in order to expose the lifting arm and leveling linkagebehind,

FIG. 3 is another view of the lifting and leveling linkage by itselfwith the lift cylinder removed and looking at the opposite side of theapparatus from that shown in FIGS. I and 2;

FIG. 4 is a partial vertical section on the line 4-4 of FIG. 3 of onlyone side of the apparatus and showing the leveling linkage;

FIG. 5 is a bottom plan view of the unloader apparatus shown in FIG. 1,but on a larger scale, with one end of the unit broken away and theflexible boots removed; and

FIG. 6 is an exploded view of the complete unloader apparatus, lookingdown on the frame and elevating mechanism with the boot-connectingassembly tilted back and with the boots removed in order to expose theconstruction.

As in the case of the unloader shown in my prior Pat. No. 3,528,570, thepresent apparatus is designed for use in unloading railroad hopper cars,but the invention is not limited to such use. The unit consistsessentially of a lift platform or boot-connecting assembly 10, which israised from a retracted position between the rails of a railroad track12 and substantially flush therewith, to an extended position above thetrack for connecting the upper ends of a pair of unloading boots I4, l4with a pair of discharge outlets 16, 16 (FIG. I) at the bottom of thehopper of a railroad car (not shown). The boot-connecting assembly issupported on the free ends of two pairs of oppositely disposedlifting-arms l8, l8 and 18', 18', respectively, which are pivotallymounted on a fixed frame 20 between the rails of track l2. Lifting-armsl8, 18 are pivoted adjacent one of the rails and extend inwardly towardthe opposite pair of lifting-arms 18, 18', which are pivoted adjacentthe other rail so that they extend inwardly toward arms l8, 18.

A power cylinder 22, having a piston rod 23, is hinged at its oppositeends to a pair of crank-arms 24, 24', one of which is rigidly connectedto one pair of lifting-arms l8, l8 and the other to the opposite pair oflifting-arms l8, 18'. Extension of power cylinder 22 causes thelifting-arms to pivot upward lifting bootconnecting assembly 10, whileretraction of power cylinder 22 permits the lifting-arms to pivotdownward lowering the boot-connecting assembly, in substantially thesame manner as the unloader shown and described in my aforementionedpatent.

The boot-connecting assembly 10 consists in this instance of a platformor H-frame 26 having two parallel channel members 28, 28 rigidlyconnected at their centers, by a cross-piece 30, which is formed ofupper and lower plates 31, 31' (FIG. 4) spaced vertically from eachother and welded at both ends to the inner sides of channels 28, 28. Apair of rectangular, hollow coupling frames 32, 32' are slidablesupported on H-frame 26 for movement transversely of track 12. The uppersurfaces of coupling frame 32, 32' are lined with thick sponge rubbergaskets 34 for sealing the connection between the coupling frames 32,32' and the flanges surrounding the discharge outlets 16 of the hoppercar. The upper end of each boot l4, 14 is fastened to the lower edge ofa flange 36, 36' on the underside of each coupling frame 32, 32'. Thelower ends of boots l4, 14 are suitably clamped to the openings in thereceptacle (not shown) for the material.

As in my prior design, the two coupling frames 32, 32' are provided withmeans for spreading them apart after the boot-connecting assembly 10 hasbeen raised above the track [2 by lift arms l8, 18'. A simplified systemfor doing this has been devised in order to save expense and to make itpossible to position both frames 32, 32' manually simply by moving oneor the other into alignment with the discharge opening on either side ofthe car to be unloaded. To this end, a spreader bar 38 (FIGS. and 6) ispivoted at its center on a pivot pin 40 within the space between the twocenter plates 31, 31' of H-frame 26, and a link 42, 42' pivoted at eachend of spreader bar 38 connects each of the coupling frames 32, 32' tosaid spreader bar and therefore to each other, such that movement of oneis accompanied by an equal movement of the other in the oppositedirection.

Links 42, 42' extend from spreader bar 38 in opposite directions and areprovided at their free ends with fixed pins 44, 44', each of which asshown in FIG. 6 extends both above and below its corresponding link. Theupper end of each pin 44, 44' is trapped between two tabs or stops 46and 48 welded to the underside of each coupling frame 32, 32', so thatthe frames must move with pivotal movement of spreader bar 38 or wheneither of them is moved manually. The lower ends of pins 44, 44 arereceived between a pair of guide rails 50, 50' in slides 52, 52', eachwelded on the inside of the adjacent channel 28, 28 and extendingoutwardly from the cross piece of the H-frame 26.

If desired, an air cylinder 54 may be provided to spread the couplingframes 32, 32' when the lift platform 10 is raised and to draw themtogether when it is retracted between the tracks 12. Spreader cylinder54 is bolted to one of the channels 28 with its piston rod 55 connectedto the spreader assembly by means of the upper end of pin 44 on link 42,pin 44 extending upward through a hole in a bracket at the end of pistonrod 55 so that it is disposed between stops 46 and 48 on the undersideof coupling frame 32. Inverted channels 56 (FIG. 6), 56' are also weldedto the underside of the coupling frames 32, 32' adjacent theirrespective funnel portions 36, 36'. Each of channels 56, 56' is widerthan the channels 28, 28 of H-frame 26 and is disposed on its couplingframe 32 or 32' so that it fits over one of the channels 28 when thecoupling frame is in place, thereby limiting the coupling frames tomovement perpendicular to the track 12.

The fixed frame 20 of the present unloading apparataus consists of apair of parallel stringers 60, 60, formed from heavy angle iron, theadjacent ends which are connected by fixed journal rods 62, 62'.Stringers 60, 60 are long enough to span the distance between the railsof track 12 so that the ends 64 of the stringers rest on the baseflanges of the rails. Since space, or more especially verticalclearance, is a primary consideration in connection with unloaderinstallations, the ends 64 of each of stringers 60, 60 outward of therods 62, 62' are sloped upward on their undersides in order to lower theframe 20 as much as possible and at the same time providesurface-to-surface contact with both rails 12 on which they rest. Toaccomplish this, each end 64 is cut back a short distance. along theapex of its angle, so that the horizontal flange can be bent upward atabout a 15 angle. The lower corner of the vertical flange is also cut atthe same angle and then welded to the horizontal flange, formingupwardly inclined mounting surfaces 65 on the lower edges of thestringers at both ends. With the ends 64 of stringers 60, 60 resting onthe base flange of the track rails 12, the slope on the mountingsurfaces 65 lets the unloader unit as a whole sit somewhat lower betweenthe rails without interfering with the bed of the track or requiring anyspecial support for the unloader other than the track itself.Furthermore, the slope of the mounting surfaces 65 is made to correspondwith the outward slope of the track flange, so that the surfaces 65 restflush on the track flange, thereby facilitating movement of the unloaderlongitudinally of the track when it is necesary to align it with theoutlet of the car.

In the elevating mechanism at one end of the unit, the lifting arms l8,18' are rigidly mounted, as by welding, at the opposite ends of a torquetube 66' (FIG. 5), through which fits a pivot tube 68' rotatablysupported on journal rod 62'. For a reason which will become moreapparent hereinafter, torque tube 66 is rigidly fastened, as by welding,to pivot tube 68' only at one point 70' midway between lifting arms l8,l8. Pivot tube 68', which is longer than torque tube 66, extends outwardbeyond both ends thereof and is held against movement longitudinally ofpivot rod 62' by bushings 72, 72, which are interposed between each ofits ends and the vertical flange of the adjacent stringer 60. Assemblybolts 74, 74 extend through stringers 60, 60 and are threaded into eachend of journal rod 62' for rigidly securing the stringers 60, 60thereto.

Referring to FIGS. 1 and 2, the crank-arms 24, 24 at opposite ends ofthe unit, by which lift cylinder 22 raises lifting arms l8, 18' in amanner similar to that shown in my prior Pat. No. 3,528,570, are eachwelded to one end of the corresponding pivot tube 68, 68'. Eachcrank-arm has a hinge 76, 76' pivotally connecting it to lift cylinder22 by means of hinge pins 78 and 80. In this instance, hinge 76 consistsof a pair of parallel side plates 82, 82, disposed on opposite sides ofcrankarm 24. intermediate hinge pins 78 and 80 and between plates 82, 82is mounted a cylindrical abutment 84 on a bolt 86 extending through bothside plates 82, 82. Bolt 86 holds the side plates rigidly togetheragainst spacers on hinge pins 78 and 80 in order to allow the hinge 76to pivot freely about both hinge pins.

Crank-arm 24 extends inward from its pivot tube 68 in generally the samedirection as lifting arms 18, 18 and is provided at its inner end with aC-shaped bracket 88, within which the abutment 84 on hinge 76 isdisposed for limiting pivotal movement of the hinge about hinge pins 78and 80. Consequently, when the elevating mechanism is completelyretracted, hinge 76 is pivoted to its full-line position shown in FIG. 2with its abut ment 84 engaging the lower flange of bracket 88. Uponextension of lift cylinder 22, hinge 76 pivots upward about itshinge-pin 80 until abutment 84 engages the underside of the upper flangeof bracket 88, as shown in broken lines in FIG. 2. This provides thesame action that is achieved in the unloader shown in my prior patent,whereby the lift cylinder elevates itself from a re tracted positionbetween the rails 12 to a raised position where it has the requiredmechanical advantage to pivot the lifting arms l8, l8 upward in order toelevate the boot-connecting assembly 10 into engagement with thedischarge outlets l6, 16 of the hopper car.

It will be noted that the elevating mechanism at the both sides of thetrack correspond exactly, each having a torque tube 66, 66 on which thelifting arms l8, 18' are rigidly mounted, and a pivot tube 68, 68'rigidiy connected to its torque tube 66, 66' at the center 70, 70' aswell as a hinge 76, 76' by which its crankarm 24, 24' is connected tothe power cylinder 22. it will also be noted that upon expansion of liftcylinder 22, both hinges 76, 76 pivot upward until their centralabutments 84, 84' engage the upper flange of the respective brackets 88,88 on crank-arms 24, 24'. At this point, the force exerted by cylinder22 is transmitted to crank-arms 24, 24' to pivot lifting arms 18, 18 andl8, l8 upward.

in order to prevent leakage around the gaskets 34 as the material in thehopper car is being unloaded, it is necessary that the lifting arms eachexert substantially equal pressure against the underside of theassembly. A rather expensive way of ensuring that equal pressure isapplied on both sides of the assembly is to provide a second powercylinder on the opposite side of the assembly 10 from the cylinder 22shown in FIG. 5. However, in order to avoid a costly expedient such asthis, the present lifting assembly is designed so that even though thesingle cylinder 22 is mounted on one side of the unit, the force exertedby it is distributed evenly on both sides. Such equal distribution offorce is achieved by connecting the pivot tubes 68 and 68' at thecenters 70, 70' of torque tubes 66 and 66', respectively, so that thetorque transmitted by pivot tube 66 from crank arm 24 is applied to thetorque tube 68 at a point equidistant from each of lifting arms l8, 18,while the torque transmitted by pivot tube 66' is applied to torque tube68' at a point equidistant from each of lifting arms l8, 18'. Therefore,exactly the same force is exerted on each of the arms at each side ofthe unloader, as if the cylinder itself were mounted midway between thetwo lifting arms in each pair. On the other hand, the forces on theopposing lifting arms at opposite ends of the lift cylinder arenecessarily explained because the cylinder is mounted between them andexerts equal forces of action and re-action on them in oppositedirections, as in the unloader of my prior patent.

The free end of each of the four lifting arms l8, 18' is provided with aroller on the inner side of each arm. Rollers 90 ride within thechannels 28, 28 of the H-frame 26 in boot-connecting assembly 10. Asbest shown in FIG. 4, channels 28, 28 are C-shaped in crosssection andare disposed so that they open outwardly to receive the rollers 90 ofthe lifting arms. When lifting arms 18, 18' are pivoted upward uponextension of lift cyiinder 22, their outer ends move lengthwise ofchannels 28, 28, and as will be more apparent hereinafter, means similarto that shown in my prior patent are provided for keeping theboot-connecting assembly 10 as a unit centered between the rails oftrack 12. In addition, it is also necessary to provide means forpreventing the boot-connecting assembly 10 from tilting transversely oftrack 12 when more resistance to lifting the assembly is encountered bythe two sets of lifting arms l8, 18 or l8, 18' at one end of the unitthat at the other.

One of the most important aspects of the present unloader is thedevelopment of a mechanically simpler leveling system for preventingsuch tilting than the one employed in my prior design. The conceptunderlying the present leveling system is the use of the well knownprinciple of a parallelogram. in this instance the platform for theboot-connecting assembly and the fixed frame of the unloader in effectform two of the parallel sides of a parallelogram. However, it isessential in unloading apparatus of this kind for the platform or H-frame 26 to lie in its retracted position in the same plane with thefixed frame 20, so that the coupling frames 32 and gaskets 34 do notproject above the top of the rails 12. Consequently, if the H-frame 26itself is used as one of the parallel sides of the figure, there is aconsiderable distance through which the lift platform must be raisedbefore the parallelogram can effectively prevent it from tilting to oneend or the other. Such undesired tilting action results from the factthat the parallelogram thus formed is completely collapsed when the liftplatform is retracted with all members of the parallelogram lying in thesame plane. In that condition, if the platform 26 were part of theparallelogram, any looseness of the joints of the elevating mechanismwould permit the platform to tilt to one end or the other as it startsto rise and then to snap up violently to a horizontal position. Erraticmovement of this kind is unacceptable, not only because it is dangerous,but also because it causes excessive wear of the parts and canpermanently damage them.

in order to overcome this difficulty, a system of links, indicatedgenerally at 91 (FIGS. 2 and 3), is provided in order to form aparallelogram even when the lift platform is completely retracted. Theleveling linkage 91 is separate from the lift platform of the unloaderin the sense that the platform itself does not form a part of theparallelogram relied upon for leveling purposes. However, linkage 91 isso closely coordinated with the lift platform that any movement thereofis simultaneously followed by a corresponding movement in the levelinglinkage. To this end, leveling linkage 91 consists of a pair of paralleltorque links 92, 92' pivotally mounted in spaced relationship to eachother along one of the stringers 60 of the fixed frame 20. One of thelinks 92 is rigidly mounted on the end of pivot tube 68' of the liftingassembly opposite the crank arm 24', and the other torque link 92 ispivotally mounted on a pivot pin 94 located on stringer 60 approximatelyone-third of the distance from pivot rod 62 to the opposite pivot rod62.

Torque links 92, 92' are relatively short so that when they are verticalthey do not project substantially above the upper rolling surface of thetrack 12. Link 92 is also disposed at a fixed angle with respect to thetwo parallel lifting arms 18', 18', such that when all the lifting arms18, 18 are pivoted down to their retracted position parallel withstringers 60, 60 as shown in FIG. 2, torque link 92 extends upward atabout a 20 angle to stringers 60, 60. A tie-bar 96 is pivotallyconnected to the free ends of links 92 and 92' at 97 and 98,respectively, such that the distance between the pivot points 97 and 98is equal to the distance between the pivot pin 94 and pivot rod 62', thedistance from pivot point 97 to pivot rod 62' being also equal to thedistance from pivot point 98 to pivot pin 94.

Mounted integrally with torque link 92, so that it pivots therewith onpivot pin 94, is a leveling arm 100, which is the same length as andparallel to, the adjacent lifting arm 18'. Since leveling arm 100remains at a fixed angle relative to torque link 92' and lifting arm 18'is fixed with respect to link 92, the upper or free ends of arms 18 and100 are held by linkage 91 in a line that is always parallel to theframe 20. Consequently, the H-frame 26 likewise remains parallel to theframe 20. The free end of leveling arm 100 is provided with a roller900, which rolls within the C-channel 28 of the H-frame 26 similar tothe rollers 90 on lifting arms 18, 18'.

lt will be apparent from the foregoing that the bootconnecting assemblyis positively held parallel to the fixed frame by the leveling linkage91, which forms a parallelogram at all times, due to the fact thattorque links 92, 92' are disposed at an angle to the arms 18' and 100,respectively, such that tie-rod 96 is held in an elevated position whenthe lifting arms 18 are completely retracted. Furthermore, when thelifting arms are fully raised upward as far as they will go, links 92,92' will be nearly perpendicular to tie-bar 96 where the levelinglinkage 91 is most effective in maintaining the boot-connecting assemblyparallel with the frame 10, thereby providing the greatest resistance toanything tending to prevent the gaskets 34, 34' on the coupling frames32, 32' from being urged into full engagement with the outlets on thecar.

It will also be appreciated that despite the fact that the surface ofthe leveling linkage 91 is to keep the boot-connecting assembly parallelto the road bed, normal tolerances and resilience of the working partsof the apparatus permits the lift platform to be forced far enough outof parallel to maintain full contact with a car that may be tiltingrelative to the track, as for example on a banked section of the roadbed.

However, in order to prevent permanent damage to any of the parts of theapparatus due to excess pressure which, for example, may be exerted bythe lift cylinder 22 when the bootconnecting platform is held at one endagainst being raised, while being free to move up ward at the other end,it is desirable to provide a safety release against excess bending ofthe structure. Such a release is readily achieved in the present designsimply by providing means for releasing the parallelogram of theleveling linkage 91 at one end of the tie-bar 96. As best seen in FIG.5, tie-bar 96 is made up of two parallel bars 102, 102 which straddlethe torque links 92, 92'. The pivotal connection 98 between tie-bar 96and torque link 92' consists of a clevis pin which passes through bothbars 102, 102 as well as link 92' and is held in place by means of acotter pin. The opposite ends of bars 102, 102 are resiliently heldtogether by a spring assembly consisting of a bolt 104, which extendsfreely through both bars 102, 102 with one end projecting laterallybeyond one of the bars 102. A coil spring 106 is placed on the other endof bolt 104 and held in place by a nut, which may be turned down on bolt104 in order to increase the pressure exerted by spring 106 on theadjacent bar 102.

Tie-bar 96 is pivotally connected to torque link 92 at 97 by means of apair of inwardly projecting tapered studs 108, 108, one of studs 108being mounted on the facing side of each of the bars 102, 102. Studs108, 108 are normally held within outwardly facing sockets in theopposite ends of a bushing 110 in the outer end of torque link 92, thesockets in bushing 110 into which studs 108, 108 fit being desirablytapered to correspond to the taper of the studs. it will be apparentthat upon exertion of a force on tie-bar 96 sufficient to spread bars102, 102 apart against the pressure of spring 106, due to the cammingaction of tapered studs 108, 108 on bushing 110, studs 108, 108 will beforced out of their sockets, thereby breaking or releasing theparallelogram and permitting the lift platform of the unloader to dropto one side under the pressure distorting it in that direction. Whenthis occurs, the cause of the difficulty must be determined. This maybe, for example, a heavy object resting on one side of the lift platformpreventing it from lifting up on that side when the lift cylinder isoperated. With the cause of the trouble corrected, the tie-bar 96 may bereadily reconnected to the torque link 92 and the unloader againoperated normally.

It should be noted that a centering link 112 is pivotally connectedatone end to the mid-portion of leveling arm 100 and at its other end tothe H-frame 26 of the lift-platform or boot-connecting assembly 10.Centering link 112 simply prevents the lift-platform from movingtransversely of the railroad track 12 on the rollers 90 of lifting arms18, 18' and could, if desired, be mounted on any of the lifting arms, asin the apparatus shown in my prior Pat. No. 3,528,570.

Power cylinder 22 is a doubleacting, hydraulically damped pneumaticcylinder having air supply lines 115 and 116 (FIG. 6) connected to acontrol valve 118 mounted at a suitable control station adjacent theunloading station. Air under pressure is supplied to control valve 118from a suitable source (not shown) through a supply line 120. Controlvalve 118 can be operated to furnish air under pressure to either end ofcylinder 22 while exhausting the opposite end, thereby raising andlowering the lift-platform.

I claim:

i. In a lifting assembly having a fixed frame defining a plane, at leastone pair of oppositely disposed lifting arms of equal length, each ofsaid arms being pivotally mounted at one end to said fixed frame andhaving a free end, a movable platform supported on the free ends of saidlifting arms and movable thereby from a position substantially withinsaid plane to an elevated position above said plane, and a powercylinder operatively connected at one end to one of said lifting armsand at its other end to the opposite one of said lifting arms forpivoting said lifting arms in opposite directions upon actuation of saidpower cylinder,

leveling means for equalizing the pivotal movement of each of saidlifting arms comprising in combina tion therewith,

at least one leveling arm disposed parallel to one of said lifting armsand pivoted to said fixed frame, said leveling arm being equal in lengthto said one lifting arm and having a free end in sliding engagement withsaid movable platform,

a first torque link rigidly connected to said one lifting arm at a fixedangle thereto for pivotal movement therewith. a second torque linkrigidly connected to said leveling arm at a fixed angle thereto equal tosaid firstmentioned angle for pivotal movement with said leveling arm,and

a tie-bar pivotally connected to said torque links parallel to saidfixed frame, such that said tie-bar, torque links and fixed frame form aparallelogram,

said angles between said torque links and their respective arms beingsuch that when said lifting and leveling arms are disposed substantiallywithin said plane of said fixed frame, said links extend outward of saidplane.

2. The combination defined in claim 1, which further includes means forreleasing said parallelogram when a predetermined force is exerted onsaid movable platform tending to tilt it relative to said plane,

3. The combination defined in claim 2, wherein said means for releasingsaid parallelogram comprises a spring-loaded pivotal connection betweensaid tie-bar and one of said torque links.

4. The combination defined in claim 3, wherein said pivotal connectioncomprises a tapered stud on one of said tie-bar member and torque-linkmember and extending laterally thereof, a socket in the other of saidmembers within which said stud is received and spring means for urgingsaid stud into said socket, whereby an excessive force exertedlongitudinally between said members results in a lateral forcesufficient to force said stud out of said socket due to the cammingaction of said tapered stud in said socket.

5. in a lifting device having a pair of parallel lifting arms pivotallymounted on a common axis in spaced relation to each other in order toprovide open access between them and having power means for raising bothof said lifting arms simultaneously by exerting power at a single pointalong said axis that is closer to one of said lifting arms than theother,

drive means for transmitting such power from said power means along saidaxis to said lifting arms comprising in combination therewith,

an elongated pivot member journalled for pivotal movement about saidaxis and driven by said power means. and

a torque tube co-axially supported on said pivot member for pivotalmovement therewith, said lifting arms being fixed to said torque tubefor pivotal movement therewith,

said torque tube being rigidly fastened to said pivot member only at themidpoint between said lifting arms in order to distribute the forceexerted by said power means equally to said lifting arms.

6. The combination defined in claim 5, wherein said pivot member isdisposed within, and supports, said torque tube along its entire length.said pivot member being pivotally supported at both ends and having acrank-arm extending laterally therefrom adjacent one end, said powermeans comprising a power cylinder operatively connected at one end tosaid crank-arm.

7. The combination defined in claim 6, in which said lifting deviceincludes a second pair of parallel lifting arms disposed opposite saidfirst pair and pivotally mounted on a second axis in correspondinglyspaced relation to each other in order to maintain open access betweensaid lifting arms,

said second pair of lifting arms having drive means corresponding tothat for said first-mentioned pair of lifting arms and including asecond pivot member rigidly connected to a second torque tube at themid-point between its lifting arms, said second pivot member having acrank-arm disposed opposite said first-mentioned crank-arm with theopposite end of said power cylinder connected thereto, such that uponextension of said power cylinder pressure is exerted by said cylinder onsaid crankarms in equal and opposite directions,

the power applied to said pivot-members by said cylinder beingtransferred to said lifting arms through the mid-points of said torquetubes, thereby ensuring equal lifting effort by each of said liftingarms.

i IF I I I?

1. In a lifting assembly having a fixed frame defining a plane, at leastone pair of oppositely disposed lifting arms of equal length, each ofsaid arms being pivotally mounted at one end to said fixed frame andhaving a free end, a movable platform supported on the free ends of saidlifting arms and movable thereby from a position substantially withinsaid plane to an elevated position above said plane, and a powercylinder operatively connected at one end to one of said lifting armsand at its other end to the opposite one of said lifting arms forpivoting said lifting arms in opposite directions upon actuation of saidpower cylinder, leveling means for equalizing the pivotal movement ofeach of said lifting arms comprising in combination therewith, at leastone leveling arm disposed parallel to one of said lifting arms andpivoted to said fixed frame, said leveling arm being equal in length tosaid one lifting arm and having a free end in sliding engagement withsaid movable platform, a first torque link rigidly connected to said onelifting arm at a fixed angle thereto for pivotal movement therewith, asecond torque link rigidly connected to said leveling arm at a fixedangle thereto equal to said firstmentioned angle for pivotal movementwith said leveling arm, and a tie-bar pivotally connected to said torquelinks parallel to said fixed frame, such that said tie-bar, torque linksand fixed frame form a parallelogram, said angles between said torquelinks and their respective arms being such that when said lifting andleveling arms are disposed substantially within said plane of said fixedframe, said links extend outward of said plane.
 2. The combinationdefined in claim 1, which further includes means for releasing saidparallelogram when a predetermined force is exerted on said movableplatform tending to tilt it relative to said plane.
 3. The combinationdefined in claim 2, wherein said means for releasing said parallelogramcomprises a spring-loaded pivotal connection between said tie-bar andone of said torque links.
 4. The combination defined in claim 3, whereinsaid pivotal connection comprises a tapered stud on one of said tie-barmember and torque-link member and extending laterally thereof, a socketin the other of said members within which said stud is received andspring means for urging said stud into said socket, whereby an excessiveforce exerted longitudinally between said members results in a lateralforce sufficient to force said stud out of said socket due to thecamming action of said tapered stud in said socket.
 5. In a liftingdevice having a pair of parallel lifting arms pivotally mounted on acommon axis in spAced relation to each other in order to provide openaccess between them and having power means for raising both of saidlifting arms simultaneously by exerting power at a single point alongsaid axis that is closer to one of said lifting arms than the other,drive means for transmitting such power from said power means along saidaxis to said lifting arms comprising in combination therewith, anelongated pivot member journalled for pivotal movement about said axisand driven by said power means, and a torque tube co-axially supportedon said pivot member for pivotal movement therewith, said lifting armsbeing fixed to said torque tube for pivotal movement therewith, saidtorque tube being rigidly fastened to said pivot member only at themid-point between said lifting arms in order to distribute the forceexerted by said power means equally to said lifting arms.
 6. Thecombination defined in claim 5, wherein said pivot member is disposedwithin, and supports, said torque tube along its entire length, saidpivot member being pivotally supported at both ends and having acrank-arm extending laterally therefrom adjacent one end, said powermeans comprising a power cylinder operatively connected at one end tosaid crank-arm.
 7. The combination defined in claim 6, in which saidlifting device includes a second pair of parallel lifting arms disposedopposite said first pair and pivotally mounted on a second axis incorrespondingly spaced relation to each other in order to maintain openaccess between said lifting arms, said second pair of lifting armshaving drive means corresponding to that for said first-mentioned pairof lifting arms and including a second pivot member rigidly connected toa second torque tube at the mid-point between its lifting arms, saidsecond pivot member having a crank-arm disposed opposite saidfirst-mentioned crank-arm with the opposite end of said power cylinderconnected thereto, such that upon extension of said power cylinderpressure is exerted by said cylinder on said crank-arms in equal andopposite directions, the power applied to said pivot-members by saidcylinder being transferred to said lifting arms through the mid-pointsof said torque tubes, thereby ensuring equal lifting effort by each ofsaid lifting arms.